linux-kernel - Re: media: dvb-usb-v2/gl861: ensure USB message buffers DMA'able

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Message-ID: <d2465376-4b3e-7d3d-86d2-0cd8d7543520@gmail.com>
Date:   Tue, 3 Jul 2018 21:07:07 +0900
From:   Akihiro TSUKADA <tskd08@...il.com>
To:     Colin Ian King <colin.king@...onical.com>,
        Mauro Carvalho Chehab <mchehab+samsung@...nel.org>,
        linux-media@...r.kernel.org, Antti Palosaari <crope@....fi>
Cc:     "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: media: dvb-usb-v2/gl861: ensure USB message buffers DMA'able

Hi,
thanks for the report.

>  47        buf = NULL;
> 
> Condition rlen > 0, taking false branch.
> 
>  48        if (rlen > 0) {
>  49                buf = kmalloc(rlen, GFP_KERNEL);
>  50                if (!buf)
>  51                        return -ENOMEM;
>  52        }
> 
>  53        usleep_range(1000, 2000); /* avoid I2C errors */
>  54
>    CID 1470241 (#1 of 1): Explicit null dereferenced (FORWARD_NULL).
> var_deref_model: Passing null pointer buf to usb_control_msg, which
> dereferences it.
> 
>  55        ret = usb_control_msg(d->udev, usb_rcvctrlpipe(d->udev, 0),
> req, type,
>  56                              value, index, buf, rlen, 2000);
> 
> 
> The assignment of buf = NULL means a null buffer is passed down the usb
> control message stack until it eventually gets dereferenced. This only
> occurs when rlen <= 0.   I was unsure how to fix this for the case when
> rlen <= 0, so I am flagging this up as an issue that needs fixing.
> 

Since rlen is an u16, null pointer is passed only when rlen == 0,
so I think it is not a problem,
but I am OK to add a guard in order to make scan result clean.

regards,
Akihiro